Synchronization of illumination source and sensor for improved visualization of subcutaneous structures

ABSTRACT

System and method are described for synchronizing a pulsed source of the near infrared illumination used in visualizing subcutaneous structures with the background illumination normally extant in medical treatment settings that allow both enhanced image acquisition and use of higher power pulsed infrared illumination sources.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.11/548,313 filed Oct. 11, 2006 (pending), which claims the benefit ofU.S. Provisional Application No. 60/786,880 filed Mar. 28, 2006, thedisclosures of which are incorporated herein by reference.

STATEMENT OF GOVERNMENT INTEREST

The invention described herein was made under a Cooperative Research andDevelopment Agreement number 02-161-ML-01 with the Department of The AirForce. The Government of the United States has certain rights in theinvention.

FIELD OF THE INVENTION

The invention described herein relates generally to medical devices andprocedures for access to human or animal vasculature, and moreparticularly to system and method for enhanced visualization ofsubcutaneous structures under ambient lighting from fluorescent,incandescent, light emitting diode (LED) or other illumination source.

BACKGROUND OF THE INVENTION

The use of near infrared (NIR) radiation for diagnostic procedures inthe human body has traditionally been limited by the inability totransmit NIR radiation into and through the body and extremities (see,for example, Handbook of Optical Biomedical Diagnostics, V Tuchin, Ed,SPIE Press, Bellingham Wash. (2002)). U.S. Pat. No. 6,230,046 to Craneet al showed that with sufficient amplification, transmitted NIRillumination may be used for both diagnostic and medical proceduresinvolving vascular imaging. However, with this amplification, theimaging system must use a darkened environment and bandpass filters tolimit interference from background light typically extant in medicalsettings.

The use of an NIR sensor and reflected or transilluminated NIR light toview both dermal and subdermal structures in the body is limited by theamount of light that is interacted with the body and is available forimaging on a detector, such as those commonly used in the art includingcharged coupled device (CCD) arrays, metal on silicon (MOS) arrays orimage intensifier tubes (IIT) or combination of these. Image quality orresolution is directly related to the amount of light with imageinformation that reaches the detector after interaction with the bodyminus the light that is captured that does not interact with the body.Light that does not contain image information is considered noise anddegrades the image. For example, sunlight that is reflected from thesurface of skin and entering the detector optics degrades the image indirect relationship to the amount of light intercepted by the detector.

Optical filtering to restrict the pass band of the detector to the lightemitted by the illumination source according to Crane et al showed thatNIR sensitive detectors could be used to image both dermal and subdermalstructures such as veins and arteries. This works well for manyillumination sources of visible lighting, but has limited applicabilityfor sources that emit light in that portion of the NIR spectrum near orwithin the band used for image formation. Typical visible illuminationsources such as fluorescent light bulbs have strong emission lines atwavelengths between 800 and 900 nm that represent noise in an NIRsubdermal imaging system.

SUMMARY OF THE INVENTION

The invention described herein solves or substantially reduces incritical importance problems in the prior art by providing system andmethod for NIR imaging of subcutaneous structures under full fluorescentlighting including use of higher power illumination sources totransilluminate thicker human tissue. System and method are describedfor synchronizing a pulsed source of the NIR light used in visualizingsubcutaneous structures with the background lighting normally extant inmedical treatment settings that allow both enhanced image acquisitionand use of higher power pulsed infrared illumination sources. Thebackground lighting may also have as its source fluorescent light orwhite light LEDs used to illuminate the medical treatment procedure.

In accordance with an aspect of the invention it was recognized thatfluorescent light is emitted from a source in a full wave rectified sinewave series of peaks at a frequency of 120 Hz. The detector is timegated to eliminate extraneous light, and NIR imaging is accomplishedwhile the fluorescent lighting is extinguished at 120 Hz. When the imageillumination is captured during these small windows of darkness and neardarkness, image quality is enhanced to nearly that obtained undersubstantially complete darkness.

Pulsing the illumination source (light emitting diodes (LED), etc) andthe detector in synchronization with the background illumination (forexample, fluorescent) according to the invention allows an increase inelectrical power that can be applied to the LED illumination source(with corresponding brighter light output) and optimizes the imagingdata during the time that the background illumination is diminished orextinguished. This offers a benefit of significantly enhanced userfacility in that the imaging system can be used in a fully fluorescentroom light illumination. Standard fluorescent bulbs were used asbackground lighting in demonstration of the invention, but other pulsedsources such as visible LEDs may be used within the scope of theinvention and the appended claims.

The pulsed aspect of the invention additionally provides significantlyenhanced power levels that can be applied to the illuminating sourcewhile keeping its temperature within appropriate bounds for efficientpower conversion, e.g. in light emitting diodes. Further, this techniquesignificantly reduces the temperature of the lighting package when it isa necessary or optimal part of an illumination source that must be incontact with patients.

The invention finds use in medical procedures that require access to orimaging of subdermal structures for various medical procedures, such as,but not limited to, venous and arterial access, including access underhazardous or dimly lit conditions, detection of subcutaneous foreignstructures, placement of medical devices for injection or removal offluids or other procedures as would occur to the skilled artisanpracticing the invention, including blood sampling or administration oftherapeutic agents, the placement of a hypodermic needle for taking afluid sample from a suspected tumor or growth in the human femalebreast, which is not usually aided by real time imaging, or placement ofother surgical instruments, such as catheters, prostheses, smallendoscopic instruments and others. The invention permits continualimaging during this procedure so that placement of the medical device ismaintained within the area of interest, which is not practical withconventional x-ray imaging due to the exposure of the patient andclinicians to excessive ionizing radiation.

The invention can also be used in association with controlled pulsedvisible environmental lighting, such as pulsed white light LED lighting,wherein the pulse length and period of lighting mode is controlled.Wavelength selection can be made for visualization of selectedsubcutaneous structures, such as visualizing veins from arteries, andapplied for reflection, transillumination or backscatter modes.

The invention therefore relates to an improved medical procedure forenhancing the visualization of veins, arteries and other subcutaneousnatural or foreign structures in the body, under conditions ofartificial lighting, comprising the steps of:

-   -   providing a light source for illuminating a portion of the body        in at least one of a reflection mode and a transillumination        mode, and illuminating the portion of the body with said light        source;    -   detecting the pulsed output of the artificial lighting, whether        environmental or artificially applied in conjunction with the        practice of the method, and under which the method is performed,        and defining the maxima and minima of the output of the        artificial lighting;    -   pulsing said light source in synchronization with the minima of        the output from the artificial lighting; and    -   detecting the light from said light source reflected from or        transilluminated through the body portion.

The invention also relates to a system for enhancing the visualizationof veins, arteries and other subcutaneous natural or foreign structuresin the body, under conditions of artificial lighting, comprising:

-   -   a light source for illuminating a portion of the body in at        least one of a reflection mode and a transillumination mode;    -   first light detection means for detecting the pulsed output of        the artificial lighting, and defining the maxima and minima of        the output of the artificial lighting;    -   means for pulsing said light source and means for synchronizing        the pulsing of said light source with the minima of the output        of the artificial lighting; and    -   second light detection means for detecting the light from said        light source reflected from or transilluminated through the body        portion.

The invention further relates to a system for visualizing a structureinside a body portion, the system comprising:

-   -   an illumination source for illuminating a body portion, which        may be in the range of about 400 to 1400 nm, and which may be        pulsed in a frequency range of abut 10 Hz to 10 kHz;    -   a receiver for receiving light from the body portion during at        least two discrete temporal intervals, and a light intensifier        coupled to the receiver; and    -   a display that displays an image including information about the        structure, and, alternatively a detector for detecting        background illumination, and a source controller in        communication with the detector for selectively synchronizing        the source illumination with a temporal feature of the        background illumination, and/or a receiver controller in        communication with the detector for selectively synchronizing        the source illumination with a temporal feature of the        background illumination.

These and other aspects, objects, and advantages of the invention willbecome apparent from the following detailed description ofrepresentative embodiments thereof.

DESCRIPTION OF THE DRAWINGS

The invention will be more clearly understood from the followingdescription of representative embodiments thereof read in conjunctionwith the accompanying drawings.

FIG. 1 shows the optical power output from a typical fluorescent lightbulb with a superimposed pulse train representing the output of an LEDlight source and data acquisition times for an image acquisition systemfor NIR imaging of subdermal structures according to the invention.

FIG. 2 is a schematic of the key elements of a pulsed NIR imaging systemuseful in the practice of the invention.

FIG. 3 is a detailed schematic of the system components useful in pulsedNIR imaging according to the invention.

FIG. 4 is a pictorial representation of the NIR imaging method of theinvention.

FIG. 5 is a partial irradiance spectrum from fluorescent lightstypically used in an industrial environment.

FIG. 6 is a partial irradiance spectrum from fluorescent lightstypically used in a home environment.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, FIG. 1 shows a plot 11 of voltage versustime defining the optical power output from a typical commerciallyavailable fluorescent light bulb. Background lighting in a medicaltreatment environment may have as its source incandescent, LED, or otherpulsed illumination, as well as fluorescent illumination. The inventionis, however, described herein in consideration of fluorescent backgroundlighting as representative of the lighting under which the invention maybe operative, with the understanding that the invention can bepracticed, within the scope of these teachings and the appended claims,under conditions of other pulsed lighting.

In accordance with a feature of the invention, and consideringfluorescent background lighting as an example, it is recognized thatfluorescent illumination is produced as a full wave rectified sine wavewith a frequency of 120 Hz. If the artificial lighting is applied inconjunction with the practice of the invention, the lighting need not bea sine wave or rectified wave. The illumination is produced in pulses 13between which are defined intervals 15 during which the illumination isoff or substantially diminished in intensity. In accordance then with agoverning principle of the invention, NIR illumination of subcutaneousstructures, as from an LED source, is accomplished in pulses 16 appliedduring intervals 15. Pulsing of the NIR source is synchronized toprovide maximum NIR output when ambient (fluorescent) illumination isminimum or extinguished. The synchronization pulse also gates the NIRimaging detector so that image data is acquired only during intervals 15when ambient (room) lighting is at a minimum. A synchronizationfrequency of 120 Hz is well above the human flicker fusion frequency of30 Hz so that the images appear continuous. Optimum pulse timing andduration can be easily ascertained by one skilled in the art practicingthe invention. Depending on the type of background illumination, pulsetiming may be selected corresponding to the frequency of the backgroundthat may be in the range of from about 10 Hz to about 10 kHz. Pulseduration may be of the order of the intervals 15. In the examplerepresented in FIG. 1, the fluorescence has a cycle of about 833 msec,and permits about 211 msec (about 25%) for a duty cycle for NIR pulses16. Shorter duty cycles for NIR pulsing may be associated with largercurrents applied to the NIR source. The timing or gate width of the NIRdetector, represented by the width of pulses 16, can be varied topresent to the observer both a surface image using visible light and asubsurface image either separately or simultaneously.

Referring now to FIG. 2, shown therein is a schematic of the essentialelements of a pulsed NIR imaging system 20 for practicing the method ofthe invention as just described. In system 20, NIR source 21 is used toilluminate or transilluminate a body portion of patient 22 with imagesthereof received by NIR imaging detector 23 similarly to the methoddescribed by Crane et al. Source 21 may most usefully have wavelength inthe range of about 400 nm to abut 1400 nm, selected as would occur tothe skilled artisan practicing the invention. In accordance with thepresent invention, however, and distinct from the Crane et al method,source 21 is pulsed in order to provide images synchronized with theminima of the output from the ambient room (e.g., fluorescent, visibleLEDs) light source 24. To accomplish this, a visible detector 25 isprovided to detect the output of light source 24 and a logic and pulsingcircuit 27 interconnects detector 25 and power supply 28 to provide thesynchronized pulsing to NIR source 21.

Referring now to FIG. 3, shown therein is a more detailed schematic ofthe essential components of a pulsed NIR imaging system according to theinvention. In FIG. 3, system 30 includes an source 31 used to illuminateor transilluminate a body portion of patient 32 with images thereofreceived by NIR imaging detector 33. Source 31 is pulsed by pulsegenerator 34 through pulse amplifier 35. Visible light detector 36 isoperatively connected with pulse generator 34 and detects the light fromthe ambient visible room light source 37 in order to synchronize thepulses of NIR source 31 with the minima of the output from room lightsource 37. In a system built and operated in demonstration of theinvention, NIR source 31 was a specially built NIR light emitting diodearray manufactured by Opto Technology, Inc., pulse generator 34 was aModel 9514 manufactured by Quantum Corporation, pulse amplifier 35 was amodel PP600 manufactured by Gardasoft Vision, light detector 36 was anintensified CCD based camera manufactured by Stanford Photonics, Inc.,these items being commercially available, not considered limiting of theinvention as being selectable by the skilled artisan guided by theseteachings. Other NIR sources may be used in the practice of theinvention, including LEDs, xenon light source with a narrow band oflight transmitted to the point of interest via a light pipe or fiberoptic cable, a suitable narrow band light source or filtered, chemicalbased light source such as chemical or chemiluminescent sources orotherwise spectrally limited light broad band illumination source, thesame not considered limiting of the invention. In the demonstrationsystem, the entire electronic elements of the light detection and pulsegenerating and timing circuitry can be reduced to a single circuit boardthat can be housed in a compact housing for convenience of the clinicaloperator. A few controls that permit determination of optimum lightlevels and timing of the NIR light pulses and imaging detector wouldresult in optimum images with a minimum of interaction with the imagingsystem. Power to the NIR light source may have a significantly differentphase (as much as 60°) than that to the ambient (fluorescent) lightingbecause the two power sources may be derived from different legs of athree-phase commercial power source. The invention provides for such aphase difference by synchronizing the pulsing of the NIR illuminationsource and detector with the visible light minima using a local photodetector and pulsing circuitry as suggested in FIGS. 2 and 3.

FIG. 4 shows a pictorial representation of a clinical use of NIR imagingmethod according to the invention. In FIG. 4, a medical professional 40demonstrates the use of three different modes of visualization, namely,direct observation with image intensifier based night vision goggles(NVG) 41, an image projected on a hand held screen, such as LCD display43, or an image displayed on a computer screen 45 remote from thepatient.

State of the art NVGs have pulse regulated power supplies thataccommodate a wide range of scene illuminations, including day timelight levels. The pulsing and gating technique suggested by theinvention may also be adapted to control the response of a solid statefocal plane array, such as a charge coupled device (CCD), of manycommercial and consumer grade video recorders for use over a wide rangeof lighting conditions. Varying pulse width allows control of bothbrightness of the image with a consumer grade camcorder and the imageproduced by the NIR system described herein. Varying the width of theimaging pulse sync signal and/or phase relationship between the pulsetrain and the fluorescent lighting allows control of the NIR imagebrightness compared to the brightness of the visible light image of theskin surface of the patient.

FIG. 5 is a representative spectrum of a commercially availableindustrial fluorescent light source typical of that used in mostindustrial and hospital settings. Strong peaks in the spectrum at 812,831 and 873 nm are evident. In the practice of the invention describedherein it is therefore highly desirable, but not necessary, to avoid NIRillumination at these peaks, which is easily accomplished with opticalfilters and absorbing elements added to the NIR optical system, as wouldoccur to the skilled artisan practicing the invention and guided bythese teachings.

FIG. 6 is a portion of a representative spectrum of fluorescent lightstypically used in a home environment showing characteristic spectralcontent near 850 nm in the NIR region. In the NIR imaging, the peaks at840, 842 and 852 nm should be avoided, such as by using optical filtersand absorbing elements added to the NIR optical system.

Tests in demonstration of the invention has shown operability over avery broad range of optical powers or current and or voltage deliveredto the light generating device (LED, laser diode, or other suitablelight emitting device), and of duty cycles and phase relationshipsbetween the detector and pulsed light source and room illumination. NIRillumination levels sufficient for transillumination of the forearm ofan adult male can be achieved with a duty cycle of as little as 0.70%.Subsurface images may be produced with a duty cycle in the range from0.01% up to 30% depending upon the power levels delivered to the NIRlight source and the levels of visible room illumination. The pulsefrequency may be varied between 15 and 120 Hz and yield sufficientlycontinuous images for detection of both surface and subsurfaceanatomical features and foreign materials, diagnostic procedures, andvarious medical interventions (venous and arterial access,catherizations, probing for shrapnel or other foreign objects, or fornon-native tissue such as tumors, etc). Additional image processingtechniques, such as digital imaging processing, edge detectionalgorithms, could be applied to these systems to further enhance theimage for analysis or diagnostic applications.

The invention therefore allows NIR imaging of subcutaneous structuresunder standard ambient lighting conditions, and permits use of a highlight output NIR source in contact with the skin of a patient withoutunacceptable heating. With the higher power illumination sources, deeplyburied structures may be imaged for pathological conditions such as deepveins for thromboses, and optical absorption by intervening tissue issubstantially obviated.

The invention therefore provides novel system and method for enhancedvisualization of subcutaneous structures under normal ambient lightingconditions from fluorescent, incandescent, light emitting diode or otherillumination sources. It is understood that modifications to theinvention may be made as might occur to one with skill in the field ofthe invention within the scope of the appended claims. All embodimentscontemplated hereunder that achieve the objects of the invention havetherefore not been shown in complete detail. Other embodiments may bedeveloped without departing from the spirit of the invention or from thescope of the appended claims.

What is claimed is:
 1. A method for enhancing the visualization ofveins, arteries and other subcutaneous natural or foreign structures inthe body under artificial lighting conditions, comprising the steps of:(a) providing a light source for illuminating a portion of the body inat least one of a reflection mode and a transillumination mode, andilluminating the portion of the body with said light source; (b)detecting the pulsed output of the artificial lighting under which themethod is performed, and defining the maxima and minima of the output ofthe artificial lighting; (c) pulsing said light source insynchronization with the minima of the output from the artificiallighting; and (d) detecting the light from said light source reflectedfrom or transilluminated through the body portion.
 2. The method ofclaim 1 wherein light from said light source is in the near infrared. 3.The method of claim 1 wherein the step of detecting the light from saidlight source reflected from or transilluminated through the body portionis performed using an image detector selected from the group consistingof a charged coupled device array, a metal on silicon array, and animage intensifier tube.
 4. The method of claim 3 further comprising thestep of gating said image detector in synchronization with the pulsingof said light source.
 5. The method of claim 1 wherein said light sourceis pulsed in the range of about 10 Hz to 10 kHz.
 6. The method of claim2 wherein said light source is selected from the group consisting of alight emitting diode, a xenon source, a chemical based light source, anda chemiluminescent source.
 7. The method of claim 1 further comprisingthe step of displaying an image of the light from said light sourcereflected from or transilluminated through the body portion.
 8. A systemfor enhancing the visualization of veins, arteries and othersubcutaneous natural or foreign structures in the body under artificiallighting conditions, comprising: (a) a light source for illuminating aportion of the body in at least one of a reflection mode and atransillumination mode; (b) first light detection means for detectingthe pulsed output of the artificial lighting, and defining the maximaand minima of the output of the artificial lighting; (c) means forpulsing said light source and means for synchronizing the pulsing ofsaid light source with the minima of the output of the artificiallighting; and (d) second light detection means for detecting the lightfrom said light source reflected from or transilluminated through thebody portion.
 9. The system of claim 7 wherein light from said lightsource is in the near infrared.
 10. The system of claim 8 wherein saidsecond light detection means is an image detector selected from thegroup consisting of a charged coupled device array, a metal on siliconarray, and an image intensifier tube.
 11. The system of claim 10 furthercomprising means for gating said image detector in synchronization withsaid means for pulsing said light source.
 12. The system of claim 8wherein said light source is pulsed in the range of about 10 Hz to 10kHz.
 13. The system of claim 9 wherein said light source is selectedfrom the group consisting of a light emitting diode, a xenon source, achemical based light source, and a bioluminescent source.
 14. The systemof claim 8 further comprising means for displaying an image of the lightfrom said light source reflected from or transilluminated through thebody portion.
 15. A system for visualizing a structure inside a bodyportion, the system comprising: (a) an illumination source forilluminating a body portion; (b) a receiver for receiving light from thebody portion during at least two discrete temporal intervals; (c) alight intensifier coupled to the receiver; and (d) a display thatdisplays an image including information about the structure.
 16. Thesystem of claim 15 further comprising a detector for detectingbackground illumination, and a source controller in communication withsaid detector for selectively synchronizing the source illumination witha temporal feature of the background illumination.
 17. The system ofclaim 15 further comprising a detector for detecting backgroundillumination, and a receiver controller in communication with saiddetector for selectively synchronizing the source illumination with atemporal feature of the background illumination.
 18. The system of claim15 wherein the illumination source is in a wavelength range of fromabout 400 nm to about 1400 nm.
 19. The system of claim 18 wherein theillumination source is pulsed in a frequency range of from about 10 Hzto 10 kHz.
 20. The system of claim 16 wherein the pulse has a time ofsubstantially the temporal length of the corresponding interval.